This invention relates to a CCD arrangement which includes a semiconductor layer of a first conductivity type having a layer of insulating material such as silicon dioxide on one surface of the semiconductor layer, and a row of shift electrodes on the insulating layer which are fed with pulse train voltages displaced in phase relative to one another.
CCDs of this type have been described in detail, for example, Kosonocky in the "WESCON Technical Papers", Vol. 18, 1974, Session 2/1, pages 1-20 under the title "Charge-Coupled Devices--An Overview". They operate in such a manner that a plurality of electric charges which each correspond in size to sampled instantaneous values of an input signal and are equidistant to one another in respect of time and space, are displaced in stepped fashion along the row of electrodes in the direction towards the output of the arrangement under the influence of phase displaced pulse train voltages which are supplied to the shift electrodes. At the output of the arrangement, they are then evaluated consecutively in respect of time and used to form corresponding output signals. If one is concerned with processing analogue input signals, the sizes of the individual charges each correspond to a whole series of different instantaneous values of the input signal, whereas when digital input signals are being processed only two different logic states, "1" or "0" are represented by the presence or absence of a specific charge. In arrangements of this kind, the input signal can also consist of a radiation which falls into the substrate where it produces a formation of charge carrier pairs which differs in intensity in accordance with its own intensity. A CCD employed in this way is also referred to as an image sensor.
The evaluation, to be carried out at the output of a CCD, of the charges displaced in the semiconductor layer gives rise to difficulties, however, inasmuch as these are very small charges. In accordance with FIG. 10 (b) of the above mentioned publication, the charges are fed, for example, to an output-end diffusion zone of opposite conductivity which is previously brought to a reference potential and then released from the latter producing a state which is not bound in potential to the exterior (floating state). On the recharging of the pn-capacitance of the output-end diffusion zone and of the gate capacitance of a following read-out transistor by a charge displaced into the diffusion zone, from the read-out transistor, it is then possible to tap an output signal which exhibits only a very small voltage range produced by the recharging.